System and method for detecting the displacement of a plurality of micro- and nanomechanical elements, such as micro-cantilevers

[0001] The invention relates to a system and method for detecting the displacement of mechanical elements suitable for use in, for example, microbead-based measuring systems in which measurements are made by measuring displacement (such as deflection) and / or movement of such beams.

[0002] There is a growing interest in systems based on micro- and nanomechanical elements that are used in communication, detection of small forces and ultra-sensitive biomechanical sensors (HG Craighead, Science 290, 1532 (2000)). For example, microbeads are used to sensitively map atomic force microscopy of attraction and repulsion forces on a nanometer scale (Y. Martin, CC Willliams and KH Wickramasinghe, J. Appl. Phys. 61, 4723 (1987)), in ultra-sensitive nanomechanical biomechanical and chemical sensors (B. Ulic, D. Czapiewski, HG Carighead, P. Neuzil, C. Campagnolo and C. Batt, Appl. Phys. Lett. 77, 450 ( 2000)), for detecting charged particles (AC Stephan, T. Gaulden, A.-D. Brown, M. Smith, LF Miller and T. Thundat, Rev. Sci. Instrum 73, 36 (2002)), for recording and reading super dense data storage (P. Vettiger et al., Microelectronics Engineering 46, 11 (1999)) and in gravitational wave sensors (C. Caves, K. Thorbe, R. Drever, V. Sandberg and M. Zimmermann, Rev. Mod. Phys. 52, 341 ( 1980)).

[0003] As a rule, these systems are based on microbubbles whose one end is fixed and the other remains mobile; systems generally detect displacement and / or unfastened end movement. However, some systems are also based on beams fixed at both ends; in this case, the movement of the middle part is detected. In addition, there are also other micro- and nanomechanical constructions that are mobile and flexible, such as double-mounted blades; their 'easy' direction of movement corresponds to the turning of the paddle around the axis of the hinges connecting the paddles to the frame (usually it resembles a square racket attached to the frame on two opposing racket holders, along the axis). Other known systems use membranes that are connected to the frame with two sets of hinges, which enables two angular degrees of freedom. In the following, when we describe the general data of the invention, we will refer to micro- or nano-bars having one end fixed (clamp) and the other free end, whose deflections are measured (in this case, deflection is the displacement of the unfastened end of the microbead). However, the invention can also be used in a similar manner to other mechanical components as those described above.

[0004] For a microbead system, this deflection is several nanometers, and it may be necessary to provide a resolution greater than 0.1-1 nm, depending on the particular application. There are a number of ways to read deflection of microbubbles, such as capacitive sensors, tunnel current detection, optical interferometry, piezoelectric readings, as well as the so-called optical flux deflection technique.

[0005] Examples of microbubbles have been described, inter alia, in the following items:

Engel et al., Trends in Cell Biology, vol. 9, February 1999, pp. 77-80, "Atomie force micsoscopy: a powerful tool to observe biomolecules AT work" P. Vettiger et al., IBM J. Res. Develop., Volume 44, No. 3, May 2000, pp. 323-339. "The millipede - morę than one thousand tips for the futura AFM storage"

WO-A-01/33226 WO-A-031091458 [0006] The optical beam deflection method is the most sensitive of all, and its advantage is easy application. Figure 1 schematically shows a conventional setting according to the prior art for optical beam deflection. Light source 3 (generally a laser light source) produces a beam of light 4 (generally a laser beam in visible, ultraviolet or infrared spectrum) that is focused (i.e., either directly focused, or through a targeting system including, for example, one or more mirrors 9, etc.) on element 1 whose displacement is to be measured, for example, at the end of the micro- or nanomechanical beam. The deflection of the beam reflected from the beam is measured by photodetector 5, for example, segment photodetector, photodetector, permanent control of setting, photodetector system, etc. Generally, a segment photodetector is used, which is divided into two segments parallel to the axis of beam movement. Beam deflection generates a shift of the reflected laser point on the photodetector. Thus, the difference in photocurrents between both segments is proportional to the beam deflection.

[0007] This system is suitable for measuring both static and dynamic behavior of components / microbubbles, e.g. maximum deflection, average deflection value, reference frequency amplitude (the element can be externally driven by an excitation force oscillating at the reference frequency), the phases of motion for external drive signal, frequency, etc. Measured static displacement, amplitude, frequency, etc. they can then be referred to the object being measured and which interacts with the beam and with the signals used to stimulate the object and / or the beam.

[0008] The technique described above is applicable in practice when measuring the displacement / movement of individual components / microbeads. However, many practical applications of measuring systems for micro- and nanomechanical elements require the use of microcircuits covering most microbeads arranged in an array and operating in parallel, thus allowing greater speed and multi-functionality. Although the above described optical beam deflection technique can distribute deflections as small as 0.1 nm, the use of this technique for readings in microbead systems has proved to be a complicated procedure. Until now, light source systems have been used that had the same pitch as the microbead system. The light sources are turned on and off separately, enabling the illumination of each microbule in the system, and for sequential reading of the deflection of each microbule by a detector that constantly monitors the setting (also called a position-sensitive detector). This type of systems is described, for example, in:

[0009] Η. P. Lang et al., Applied Physics Letters, volume 72, number 3, January 19, 1998, pp. 383-385 "Sequential Position Readout from Arrays of Micromechanical Cantilever Sensors".

[0010] However, this requires sophisticated technology and accurate alignment of light beams, microbeads and photodetectors. In addition, one light beam system will only be suitable for microbead systems having the same pitch (difference between successive microbubbles).

[0011] Η. P. Lang et al., Analytica Chimica Acta 393 (1999), pp. 59-65, "An Artificial Nose Based on a Micromechanical Cantilever Array" reveals the existence of a system and method based on the sequential optical reading of the deflection of a number of microbeads in a microbead system using position sensitive detector (PSD) and a number of light sources positioned to illuminate specific microbeads. Sequential reading is possible using a time multiplexing scheme.

[0012] WO-A-OO / 75627 discusses an atomic force microscope comprising a laser beam scanning system along a series of microbeads and a system for detecting light reflected from microbeads in synchronization with scanning a light beam using drive control.

[0013] EP-A-0510895 discusses a further example of a spring offset detection system. According to one possible interpretation of the descriptions contained in EP-A-0510895, this document may describe a method and system that are largely in accordance with the introductory part of the relevant claims under this patent.

[0014] One aspect of the invention relates to a system detecting deflection, deviation or displacement, and its time variation for most components (such as micro- or nanomechanical components, e.g. micro- or nanomechanical beams attached on one or both sides, flexible membranes, etc. ) (or at least parts of such elements as the end of the beam is displaced due to its deflection) forming part of the system according to claim 1, wherein the system includes:

- a light source (e.g. a laser light source to emit visible, ultraviolet or infrared light) arranged to emit a light beam towards the system (so that a given light beam can be reflected when the light beam hits at least one of the elements of the given system, e.g. at the end of the beam element; - that a given light beam is reflected by a given element in the direction or in a manner determined by the deflection or displacement of a given element or a given part of that element); and

- position detector (basically any type of detector suitable for non-contact position detection, e.g. fixed position detection detector or segment detection detector, e.g. quarter position detector; - for example, a set of photodetectors can be used that includes a system of photodetectors having the same size or smaller than the cross-section of the laser beam; a large number of suitable devices are commercially available) arranged to obtain a light beam on the reflection of a given light beam by a given system, with the given position detector being positioned to allow obtaining output power indicating the incidence of the reflected light beam on a given position sensitive detector, wherein the given incidence is determined by or associated with the displacement of the respective element (or part of the element).

[0016] The invention assumes that the system further comprises:

- a scanning device for moving the light beam along the system so that the light beam is sequentially reflected by individual elements along the given system (by one element at a time or by a group comprising a number of elements) towards the position detector, and

- deflection detection device when a light beam is reflected by an element (or when there is 'maximum' reflection by one element and adjacent elements).

[0017] The system has been set up such that when reflection detection devices detect that a light beam is reflected by an element (or by part of this element), the corresponding first output is read as an indication of the deflection or deviation of the element (part of the element) (i.e. position the incidence of the light beam on the position-sensitive detector, for example along a certain axis, is treated as a value determining the deviation of the element).

[0018] In this way, one laser light source can be used to sequentially measure the deviation of all system components, and can also be used for systems having different strokes, without requiring the complicated methods and devices necessary for alignment. When deflecting, the light beam is sequentially reflected by one or more elements; if the beam diameter is smaller than the distance between the elements, it will be easy to associate individual elements with data obtained from the position sensitive detector (visible 'interference' will be visible in the output signal from the position sensitive detector, as there will be no reflection of the light beam towards the given detector when the light beam is directed into place between two items). However, the diameter of the light beam can be larger than the separation between the elements, and several elements can be illuminated simultaneously. In this case, the specific deflection or deflection of each element / beam can be determined using photodetector systems as a position sensitive detector; specific deviations can be determined based on the reflection pattern.

[0019] The reflection detection device includes:

- a device for detecting the intensity of light received by the position sensor in question, and

- change detection device (e.g. peak values) for a given light intensity;

wherein the system can be arranged to interpret the change data to determine when the given light intensity corresponds to the reflection of the light beam by the system element.

[0020] If the detection device within a given intensity is set to detect peak values ​​of a given light intensity, the system can be set to interpret a given light intensity as a detection of light reflection by a given element (this is probably the most practical approach, since the occurrence of the peak value obtained is essentially when the maximum portion of the laser beam is reflected by the element).

[0021] The system may further include a data processing device necessary to associate the first output signals with specific elements along the system in accordance with the changes detected for a given light intensity. This means, for example, that during beam scanning motion along the system, the first detected peak can be considered as corresponding to the reflection of the first element in the system, and the first output signal in this case will correspond to the deflection or deflection of the given element (or part of the given element).

[0022] As for scanning devices, they may include:

• device for conducting the first permanent scan (or first series of permanent scans) of the system by constantly deflecting the light beam along the given system, moving at least one scanning element (such as a mirror or the laser light source itself) from the first to the second position to make the light beam during the movement of a given scanning element from the first to the second position, it was reflected sequentially by individual elements along the given system;

• a device for storing selected positions of a given scanning element during a given first scan, wherein the selected positions data correspond to the positions at which reflections are detected by the reflection detection device (for example, detecting peaks in the intensity of light recorded by the detector); and • a device for performing subsequent scans of the microbead system by moving the scanning element from one selected position to the next selected position. Of course, the term 'jumping' should be understood broadly, and should not be interpreted in such a way that the scanning element must 'directly' jump 'from one selected position to the next selected position; essentially instead of jumping 'directly' from one selected position to the next selected pose , it can move continuously or almost continuously, but at a higher speed when it is further away from the selected position, and at a lower speed when it is closer and / or in a selected position; the important thing is that the scanning element should 'spend proportionally more time' in the selected position and / or near the selected positions than between the selected positions. For practical use, it is recommended to choose an approach that will provide relatively good results and effective scanning time, while not requiring the use of a complicated and / or expensive system designed to deflect the scanning element. This means that the scanning element can move quickly over the places where there is no reflection, and more slowly over the places where there is reflection of the light beam by the system element (for example when the detected light intensity is above a certain threshold).

[0023] This means that the first or most of the first permanent scans are used to determine which positions of the scan element cause the (maximum) reflection of the light beam by the element. This information is saved and used during subsequent scans, thanks to which subsequent scans can be made in steps, saving time (the laser beam 'spends less time' on positions where there is no reflection) and ensuring that more average information is received in places in which the elements of the system are illuminated.

[0024] The position-sensitive detector may, for example, be a set of photodetectors or a detector of constant position monitoring (also called a position-sensitive detector).

[0025] The light source may be arranged to provide a beam of light with a diameter smaller than the distance between successive elements of the system.

[0026] Another aspect of the invention is related to a method for detecting deflection, deflection or displacement of most elements (or at least parts of these elements) forming part of a system according to claim 11, especially with respect to detection of deflection or displacement of many micro- or nanomechanical elements forming part such a system. This method involves the following steps:

• directing the light beam onto the system;

• receiving with the use of an optical position detector a light beam after reflection of this light beam by a given system, and providing the first output signal from this optical position detector, the first output signal indicating the place of incidence of the reflected light beam on a given position detector, thanks to which the position incidence is determined by the deflection or movement of the corresponding element.

[0027] The invention assumes that the described method further comprises the following operations:

• moving or scanning the light beam along the system so that the light beam is sequentially reflected by individual elements along the system towards the position detector;

• detecting when the light beam is reflected by the element, and • when detecting the reflection of the light beam from the element, treating the corresponding first output signal as an indication of the deflection or offset of the element.

[0028] The act of detecting the moment of reflection of the light beam by the element may include the following steps:

• detecting the intensity of light captured by the above position detector;

• detecting changes in this intensity;

• interpreting these changes to determine when the above intensity corresponds to the reflection of the light beam by the element.

[0029] In this case, the detecting effect of the changes in the aforementioned intensity may also include detecting peak values ​​at that intensity; and the act of interpreting the changes may include an action to determine, after detecting a given intensity, whether the peak value corresponds to the reflection of the light beam by the element.

Sposób [0030] The method may further include associating, using a data processing device, the first output signals from specific elements along the system in accordance with the changes detected in the light beam intensity at the position detector.

[0031] On the other hand, the light beam scanning operation may include the following steps:

Performing the first uninterrupted scan of the system by continuously moving the light beam along the above-mentioned system, moving at least one scanning element from the first to the second position, so that the light beam can be reflected when the scanning element moves from the first to the second position through the individual elements along the system;

• saving selected positions of the above-mentioned scanning element during the first scan, wherein the selected positions correspond to the positions in which light reflections are detected by subsequent elements; performing subsequent scans based on moving the scanning element 'abruptly' from one selected position to the next selected position (the term 'abruptly' should be interpreted in a broader sense, as described above).

[0032]

Figure 1 schematically illustrates an earlier system for measuring end microbead displacement using an optical beam deflection technique.

Figure 2 schematically illustrates a system in accordance with the preferred essence of the invention (some elements may be largely identical to those used in the previous arrangement for measuring the displacements shown in Figure 1 and the same reference numbers have been used for them).

Figure 3 schematically illustrates the respective functional modules shown in this drawing.

Figure 4 is a graph showing the results of microbead deflection measurements due to temperature changes carried out in the context of the invention.

[0033] Figure 2 shows a system suitable for detecting the individual deflection of a set of micro (or nano) beams arranged in the form of a system 2 of such microbeads. As in the previous deflection measurement system, the light beam 4 is produced in the laser light source 3 and projected (when necessary using projection means, such as one or a set of mirrors 9, lenses, etc.) onto the system 2, for reflection, by one or more microbeads on the sensitive surface of the optical position detector 5, i.e. on a detector such as a photodetector, continuous position detection detector, CCD or the like which is positioned so as to provide for the first generation of a signal indicating the incident position of the reflected light beam of said position detector, whereby said incidence position is determined by the deflection of the microbule 1. In this case, with the aid of the system as illustrated in figure 2, and because the microbead is positioned to vibrate in the direction of the axis from the coordinate system, as shown in figure 2, the first output signal depends on where on the axis with the light beam will fall reflected on the sensitive surface of the position detector. Thus, the position detector may include a system or array of photodetectors positioned to provide a first output signal 51 proportional to the position along the axis of the incident light beam.

[0034] On the other hand, the system includes scanning devices 7 (only shown schematically in figure 2), for example comprising a mirror arranged on the axis so that it can rotate in a controlled manner around the z axis (for example, in the direction of the z axis in the figure 2) a mirror system comprising a mirror device linearly moving along the x axis, or a device for moving the laser light source 3 along the x axis, thanks to which the mentioned scanning devices can be introduced with the use of micro-electro-mechanical elements (The design of the appropriate means for scanning is a task that can be easily performed by a specialist who will choose the appropriate system using the most appropriate construction from the point of view of specific application, for example, due to cost and parameter requirements). In each case, the scanning devices 7 are arranged to move the light beam along the system 2 (in figure 2, moving in the x-axis direction) in such a way that the light beam is reflected successively, by individual elements 1 along said system 2, in position detector 5 as shown in figure 2).

[0035] The position detector receives a light beam and, in addition to the first output signal 51 (indicating the incident position along the z axis), it also provides a second output signal 52, whose value is a function of the light intensity received by the position detector (for example, proportional to said light intensity) . Both the first output signal 51 and the second output signal 52 are sampled using an analog-to-digital card 8, providing digital signals corresponding to the first output signals 51 and output signals 52; said digital signals are transmitted to the electronic data processing system 10, shown in more detail in figure 3. Now, as shown in Figure 2, the electronic data processing system 10 provided with information corresponding to the second output signal 52; this signal is schematically shown in figure 2, showing graph A, having a first axis A1 corresponding to the time of the scanning period and a second axis A2 corresponding to a value of light intensity measured by the position detector (i.e. for the second output 52). As shown in Figure A of Figure 2, the intensity of light changes over time; the peak corresponds to (approximately at least as discussed below) the moment when the light beam is centered on one of the microbeads 1, i.e. the moment when the reflected maximum light is directed towards the position detector 5. On the other hand, plot B has a time axis B1 and a second axis B2 corresponding to the position of the light beam along the x axis during scanning (This information can be obtained by input of the scanning means 7, indicating the position of the scanning element, such as a mirror, to deflect the light beam or similar).

[0036] Thus, comparing graphs A and B, it can be seen that when the beam of light travels along the x-axis during scanning, the position sensor 5 receives many light intensity peaks. The system is arranged such that when the peak light intensity is detected, the value corresponding to the first output signal 51 (which, for example, corresponds to the incident point of the light beam reflected on the position detector along the z axis) is taken as an indication of the deflection of the element in question.

[0037] In practice, there are several methods for associating the peak value with the deflection measured by reading the incident position of the light beam on the position detector; for example, maximum, constant and average methods.

[0038] In so-called maximum method, the deflection is measured (the first output signal is taken as the deflection indication) for the position of the laser light source for which the light intensity is detected by means of a position detector, reaches the maximum peak.

[0039] In so-called by the constant maximum method, the determined fixed position of the laser light source, corresponding to the maximum light intensity and deflection of the microbe, is detected by reading the position detector in said fixed position of the laser light source (which does not necessarily correspond to the maximum intensity of the light source received by the detector). This method is useful when there are several peaks for a single microbule, for example, due to interference processes. For example, depending on the size of the laser light beam, two peaks can be obtained, corresponding to the edges of the microbead and a small minimum size (valley) between them, corresponding to the center. Thus, it may happen that the maximum light intensity does not correspond to the moment when the light beam reflects off the "center" of the microbead; the fixed method can therefore be useful to check if the position readings correspond to the moment when the light beam (approximately) is reflected from the center of the beam.

[0040] The so-called the average method can also avoid problems of several peaks and improve the signal-to-noise ratio. This method determines the average value of the deflection signal for all light intensities higher than the defined threshold value, corresponding to the selected width of each peak value. In other words, the light intensity values ​​corresponding to the positions of the laser light source along the "width" of the peak value are used as a function of the balance to determine the average beam deflection.

[0041] The process is schematically illustrated in figure 3, showing how a position detector, comprising reflected light detection devices 11, provides the first and second output signals to the electronic data processing system 10. A second output signal is received at module 111 of said reflected light detection devices 11; said module 111 has been installed for detecting the light intensity received by said position detector (this light intensity may correspond to the level of the second output signal 52). Electronic data processing devices 112 are designed to detect changes in said light intensity, and particularly to detect peak values. The system is set up so that it can interpret these peak values ​​as deflections of the light reflecting element. Thus, when module 112 detects a peak value, it will start sampling module 13, which will get the current beam 1 deflection value at that particular moment.

[0042] Further data processing devices 12 are positioned, inter alia, to associate subsequent samples of the first exits with specific microbubbles 1 along the system in accordance with the detected changes in said light beam intensity in coordination with the scanning means.

[0043] Since all relevant signals can be fed to the electronic data processing system 10, sophisticated algorithms can be used for interpretation and scanning.

[0044] Figure 3 also schematically illustrates scanning devices 7, including devices 71 for performing the first system scan, by continuously moving the light beam 4 along said system, moving at least one scanning element 72 (such as a rotating or linearly moving mirror or a direct source of laser light) from the first to the second position, in order that the light beam, during the movement of said scanning element 72 was successively reflected by individual elements 1 of the aforementioned system 2. The scanning devices further include devices 73, intended for recording selected positions of said scanning element (each position corresponding to a specific point of axis B2 of Figure 2 of Figure 2) during the first scanning of said selected positions corresponding to positions in which light reflections are detected by reflected light detection devices (e.g. peak light intensity as explained above). Finally, devices 74 are provided for carrying out subsequent scans of the microbead system by gradually moving the scanning element 72 from one selected position to another in accordance with stored data.

[0045] The invention has proved its feasibility in practice for use in measuring deflections of individual microbeads of the microbead system. The following is an example of how the invention was used in practice to measure deflection of a microbead system consisting of three silicon microbeads, separated by 250 [mu] m. Each of the beams was 200 pm long, 50 pm wide and 1 pm thick. In this particular application, the deflection of the microbeads showed a dependence on the local temperature based on the principle of the bimetal effect: The upper surface of each of the microbubbles was covered with a 20 nm thick layer of gold, as a result of which temperature changes near the microbeads bent them due to different coefficients of linear expansion of the gold layer and silicon. For example, an increase in local temperature causes a greater expansion of gold relative to silicon, which causes the beams to bend downwards and, conversely, a decrease in temperature causes the beams to bend upwards. To test this principle, a Peltier chamber located close to the system was used to cool and heat the microbubbles. The temperature was measured with a thermistor close to the system and an external temperature controller was installed to control the temperature from outside.

[0046] The deflection detection of the microbeads was carried out by the above-described optical method of testing the deflection of the beams, in which the laser beam from the laser diode was focused at the end of the microbead using lenses; the laser beam reflected from the microbeads was collected on the position detector. Scanning of the incident light beam onto the system was carried out by moving the laser light source using a voice coil based system (namely V-106.2S scanning systems supplied commercially by Physik Instrumente (Pl) GmbH & Co.KG). Of course, it is also possible to use other scanning systems based on motorized micro-positioning stages, and piezoelectric systems can also be used.

[0047] The scanning system moves the incident laser beam along the microbead system. The test configuration was similar to that shown in figure 2. The signals from the position detection photodetector were connected to an analog-to-digital card to enable processing by the software and to present the visualization in real time using a computer (PC). Similarly, the scanning was controlled by software.

[0048] The data collection system continuously measures the output signals from the position detector (namely, light intensity and incident position of the light beam) as well as the associated position of the laser light source.

[0049] First, an initial quick scan (of mm / sec) was performed along the x axis of the laser light source, covering the entire width of the system. As explained above, when a laser beam hits the microbead of the system, a significant increase in light intensity is detected in the photodetector. Thus, after the first scan, light intensity is obtained as a function of the position of the laser light source. Peak light intensity values ​​were obtained for such positions of the laser light source at which the laser light beam falls on the ends of the microbeads. Subsequent scans are carried out more slowly in such positions of the laser light source at which reflection above the threshold value was detected (this improves the "signal to noise" ratio and optimizes the time for moving the laser). The deflection of the respective microbead was measured by reading the position signal along the axis of the reflected laser beam at the detector position when the laser beam falls on the microbead surface.

[0050] This was determined absolutely by determining the threshold value of light intensity. Light intensity values ​​higher than the threshold were considered to mean that the laser light fell on the microbead at least partially. Thus, each peak of light intensity above the threshold was considered to correspond to such a position of the laser light source at which the laser light beam falls on the microbead (as a result, the threshold of higher light intensity will mean sharper peaks of light intensity).

[0051] The deflection of each microbead can be determined using one of the three methods (i.e. maximum, constant, average method) described above (the average method was used in the example).

[0052] Figure 4 is a graph showing deflections of three microbeads (silicon + gold) due to system heating (downward deflection, corresponding to period I of the graph) and cooling (upward deflection, corresponding to the period of II graph). Each curve corresponds to one micro-bar.

[0053] Throughout the description and specification claims, the word "includes" and words such as "including" are not intended to exclude other appendices, subassemblies, integers or steps.